Airworthiness Directives; Boeing Model 747-100, -200, and -300 Series Airplanes

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-100, -200, and -300 series airplanes. This action requires repetitive inspections to detect fatigue cracking in the upper deck floor beams located at certain body stations, and repair, if necessary. This amendment is prompted by a report by the manufacturer that, during a fatigue test, the upper chord and web of the upper deck floor beams located at body stations (BS) 340 and 360 were found severed at approximately 34,000 total flight cycles. Another report by an operator indicated that a severed upper chord and web were found in the upper deck floor beam at BS 380 at approximately 33,000 total flight cycles. In addition, cracking was found at multiple fastener hole locations. The actions specified in this AD are intended to prevent failure of the upper deck floor beams at certain body stations due to fatigue cracking, which could result in rapid decompression and consequent reduced controllability of the airplane.